1. Field of the Invention
The present invention relates to a method of manufacturing a group III nitride semiconductor layer bonded substrate in which a group III nitride semiconductor layer and a different-composition substrate different in chemical composition from the group III nitride semiconductor layer are bonded with each other. The group III nitride semiconductor layer bonded substrate obtained by the manufacturing method according to the present invention is suitably used for manufacturing a semiconductor device.
2. Description of the Background Art
A group III nitride semiconductor substrate such as an Al1-xGaxN (0≦x≦1) substrate is suitably used for a semiconductor device, however, manufacturing cost thereof is extremely high. Accordingly, manufacturing cost of a semiconductor device including the group III nitride semiconductor substrate is extremely high, which seems to be derived from a method of manufacturing a group III nitride crystal semiconductor substrate.
Specifically, as hydride vapor phase epitaxy (HVPE), metalorganic chemical vapor deposition (MOCVD), sublimation, or other vapor phase deposition is employed to grow a crystal on the group III nitride semiconductor substrate, the crystal is grown slowly. For example, a crystal growth period of approximately 100 hours can only provide approximately 10 mm thick group III nitride semiconductor crystals. Crystals having such a thickness only allow a small number of (e.g., approximately 10) approximately 200 μm to 400 μm thick, group III nitride semiconductor substrates to be cut out therefrom.
If a group III nitride semiconductor layer to be cut out from the group III nitride semiconductor crystals is reduced in thickness to provide an increased number of group III nitride semiconductor substrates, however, mechanical strength is lowered and the substrate cannot be free-standing. Thus, there is a need for a method for reinforcing the thin group III nitride semiconductor layer cut out from the group III nitride semiconductor crystals.
An exemplary method of reinforcing a group III nitride semiconductor layer includes a method of manufacturing a substrate by bonding a group III nitride semiconductor layer with a different-composition substrate different in chemical composition from the group III nitride semiconductor layer (hereinafter, referred to as a group III nitride semiconductor layer bonded substrate). Japanese Patent Laying-Open No. 2006-210660 (Patent Document 1) discloses, as such a method of manufacturing a group III nitride semiconductor layer bonded substrate, a method of manufacturing a semiconductor substrate including the steps of implanting ions in the vicinity of a surface of a first nitride semiconductor substrate, layering the first nitride semiconductor substrate on a second substrate such that a surface side thereof faces the second substrate, subjecting the two layered substrates to heat treatment, and peeling most of the first nitride semiconductor substrate off from the second substrate such that an ion-implanted layer being defined as a boundary.